1. Field of the Invention
The present invention relates to a locking structure which, once a cylindrical building member locks a mating cylindrical member, prevents the locked cylindrical members from becoming loose or dislocated.
2. Description of the Related Art
FIG. 15 is a perspective view showing an essential part of an example gate pillar made of a metallic cylindrical member for building and a cover 2 made of such materials as plastics and fitted at the top of the pillar. The gate pillar 1 is a square cylinder, and the cover 2 comprises a square-cylindrical insertion portion 2a to be fitted into the pillar 1 and a cover portion 2b covering the top surface of the gate pillar 1.
The insertion portion 2a, after being pushed into the pillar 1 by a single pushing action on the part of a worker, is firmly fitted in the pillar 1 in an elastically compressed state which, combined with the cover portion 2b, prevents ingress of rain water into the interior of the pillar 1.
FIG. 16 is a perspective view of another example of a cylindrical metal member for building, in which a corner joint 3 made of an L-shaped cylindrical member is fitted at both ends with a cylindrical beam member 4 and a cylindrical pillar member 5 to form a corner portion of a sash.
In this case, too, the beam member 4 and the pillar member 5 are fitted elastically into the corner joint 3 by a single insertion operation.
The gate pillar 1 receives impacts from the door as it is opened and closed, and the impacts cause the cover 2 to gradually float degrading the appearance of the gate pillar 1.
When the corner joint 3 is applied such impacts, the similar problem also occurs causing loosening and displacement of the beam member 4 and the pillar member 5.
There have been demands for a holding means to prevent the cylindrical locking structures from becoming loose and displaced. But no such appropriate means have been available.
The present invention is designed to solve these problems and to provide an inexpensive locking structure that is very easy to install and can reliably prevent itself from getting loose. It is also an object of this invention to provide a locking structure machining apparatus that can machine the locking structure highly efficiently and inexpensively.